1. Field of the Invention
The present invention relates to controlling the operating lights of a towed vehicle (i.e. trailer) according to the operating lights of a towing vehicle.
2. Description of the Related Art
When a towing vehicle (or tractor) tows a trailer, camper, disabled vehicle, or the like (hereinafter collectively referred to as "trailers"), it is necessary to provide and actuate the trailer's lights in such a way that they are slaves and the tractor vehicle lights are masters. Lights commonly provided on trailers include: running lights for night driving; stop or brake lights; and intermittently flashing lights, which serve for turn signals when operated individually or for hazard lights when operated synchronously.
The trailer's lights must duplicate the information of the tractor vehicle's lights. However, the trailer lights need not duplicate the lighting system of the tractor vehicle. Two lighting systems currently exist--the American system and the foreign system.
The foreign system includes three rear lamps on the left and three on the right. One left-right lamp pair is for running lights, the second pair is for stop lights, and the third pair is for turn signals. With three lamps, the three basic lighting functions of run, brake, and turn are separate. The three lamps may be located in separate lamps, but often the running and stop lamps for one side comprise two filaments integrated within a single lamp.
On many American cars and trucks, the brake and turn signals are often combined. That is, the brake and turn lights use the same lamp filament pair of lamps (i.e., one left and one right). When the brake and turn signal are simultaneously activated one light flashes on-off just as it does when only the turn signal is applied on that side, while the corresponding light on the other side of the vehicle stays continuously luminated. The running lights are independent, as with foreign system. Because the turn signal lamps are also used for hazard lights or "four-way flashers", the use of one lamp per side for indicating both turn and brake does not allow the simultaneous hazard and brake lights.
Trailers typically use the American system of having only two lamps per side, often with a signal lamp having two filaments. When the tractor automobile or truck has a different system, the activation of the two light systems, of tractor and trailer, must be coordinated.
One system for interconnecting the lighting system of tractor and trailer vehicles is disclosed by John Schroeder in U.S. Pat. No. 4,405,190. Schroeder's device is an electrical connector into which are plugged cables from both the tractor and trailer. The connector has internal interconnections. This invention has no active or logical devices.
Another consideration in trailer lighting is power drain. If the trailer lights are driven by wires attached to the tractor vehicle's lights, voltage drop caused by the wiring resistance may prevent the trailer lights from being sufficiently illuminated (and excessive current draw can also cause improper signaling of the tractor vehicle light system). These problems can be avoided if the voltages present at the tractor vehicle lights are used as signals, and the current for driving the trailer lamps is supplied through a cable separate from the tractor vehicle's light.
U.S. Pat. No. 4,751,431, issued to James Ducote, teaches the use of electrical relays to drive the trailer lamps. The tractor operating lamp voltages activate the relay coils to close relay switches wired between the main battery and the trailer lamps.
U.S. Pat. No. 5,030,938, issued to Frederick Bondzeit, discloses a trailer lighting adapter.
The adapter uses a driver with XOR (exclusive OR) gates to drive the trailer brake and signal lights. The tractor vehicle's stop light and left-turn signal voltages are fed to the inputs of an exclusive OR gate. The stop light and right-turn signal voltages are fed to the inputs of a second exclusive OR gate. One XOR gate services the trailer's left side, and one the right. Each of the left and the right XOR logic gates consists physically of two CMOS XOR gates that are wired in parallel for the sake of added power capability, redundancy, and avoiding static discharge CMOS latch-up.
The output from either XOR is connected to the base of a power transistor. The transistor acts as a switch connecting the main battery to the trailer brake/turn lamp. When the XOR gate output goes high the respective lamp is powered through the transistor and lights.
The logic of an exclusive OR gate is such that, for either the left or right side trailer lamp, the light is not illuminated when either: both the stop light and the respective signal light of the tractor vehicle are not illuminated (both gate inputs low); or, both the stop light and the respective signal light of the tractor vehicle are illuminated (both gate inputs high). When only one of the tractor vehicle stop and signal lights are on (just one gate input high) the trailer light is illuminated. Thus, when the turn signal actuated while the brake applied, the light flashes on that side.
No other driver is disclosed by Bondzeit.
The Bondzeit device adapts foreign-style tractor vehicle lights to American-style trailer lights. When used to connect an American-style tractor to an American-style trailer, the device's XOR gates are superfluous and it acts only to reduce power drain at the tractor vehicle lamps. Although denoted "universal", the Bondzeit is incapable of adapting an American-style vehicle to a foreign-style trailer.
The Bondzeit invention requires a signal wire from the driver to each independently controllable lamp cluster on the rear of the trailer. The minimum number is three (not counting any common ground connection). Conversely, any additional independent lamp cluster would require additional wires and redesign of the circuit.